This project will investigate the mechanism of insulin stimulation of cyclic AMP phosphodiesterase and the possible changes which may occur in this regulatory system during aging. It will include biochemical and cytochemical localization of the hormone sensitive form of the enzyme in insulin target issues. Enzymological characterization of the basal and insulin stimulated cyclic AMP phosphodiesterase activities from adipose tissue will also be carried out. Studies on tissues from young, mature, and aged rats and mice will determine if there is an age related uncoupling of the hormone receptor from this possible primary metabolic site of insulin action. The cyclic AMP metabolizing enzymes in tissues from aged animals will be examined as a potential model for maturity onset diabetes in man.